Inductive core



y 1944. J. P. GLASS, JR

INDUCTIVE CORE Filed July 22, 1940 INVENTOR John 2? Glass Jr:

ATTORNEYS spacer material is Patented May 30, 1944 mnuc'nvn CORE John P. Glass, In, North Bergen, N. L, aulgnor,

by mesne assignments,

Newark, N. J.

to Maxwell Biloflky,

Application July 22, mo, Serial No. sleeve 12 Claims.

The present invention is applicable to inductive core structures, of iron core type reactance including special applications, as for instance, magnetic chokes, relays and leakage transformers.

As conducive to a clear understanding of the invention, it is noted that where the air gaps of reactances involve interspacers oi insulating material, such as impregnated paper or fiber between those faces of the magnetic circuit to be spaced thereby, it is diflicult accurately to predetermine the value of the reactance, due to the swelling of the interposed absorbent spacer material in impregnating the reactance which leads to an indeterminate increase in the width of the gap and a corresponding change in the reactance of the circuit. Even if this swelling were compensated for and the reactance of the circuit were of the desired value in the original manu- I facture or assembly of the unit, variations in reactance may occur in use, due .to magnetic pull efi'ecting compression of the interspacer, after the latter has become softened or rendered plastic due to external heat or heat evolved in operation. After the magnetic pull has been discontinued, the softened or plastic material tends to set and again to increase the air gap.

It is among the objects or the invention to provide an inductive core unit, the air gap and reactance of which may be accurately predetermined, and in use is not subject to change in magnetic characteristics, even under unfavorable conditions of operation.

Another object is to provide a reactance of v the above type, the accurate calibration of which and the maintenance of which said calibration is attained without material increase in cost of the apparatus, whether for materials or workmanship.

Another obiect is to provide an inductive core of the character noted, in which the economies and advantages of a very small air gap may be availed of without sacrifice in the close tolerance of reactance desired for constancy of operation.

A feature of the invention is the use in lieu of laminated porous or fibrous insulating material for the air gap, of a substantially impervious interspacer of high electrical resistance and desirably of low coefficient of expansion, which presents but small areas transversely of the line of magnetic flux and is accordingly traversed by but a small fraction of such flux. ,The interpreferably a rod or wire of high resistance metal, of low coefllcient of expansion. Among materials suitable for the purpose are tungsten, molybdenum, and certain 'tratively shown applied.

'netic ferrous laminations alloys, including by way of example, that alloy of nickel and chromium known as Nichrome.

- The wire is desirably of gauge slightly larger than the air gap desired and in the assembly of the reactance, it is compressed between the opposite v faces of the air gap or ifthe wire is h'arder than the iron, indents the latter, the pressure being applied until a meter reading shows the appa- "ratus' tohave the desired reactance, whereupon the unit is impregnated.

In the accompanying drawing in which are shown one or more of various possible embodiv ments or the several features of the invention,

Fig. 1 is a dropped perspective view of the constituent elements making up one embodiment of reactance, 1

Fig. 2 is a perspective view or the assembled unit,

Fig. 3 is a transverse sectional view, takenon the line 3-3 of Fig. 2

Fig. 4 is a transverse sectional view taken along the line H of Fig. 1,

Fig. 5 is an enlarged sectional view taken on line 5-5 01' Fig. 4, and

Fig. 6 is a view similar to Fig. 5 of a slight modification.

Referring now to the drawing, there is shown in Fig. 1, a generally conventional form of reactance core to which the invention is illus- The core is shown as comprising two complementary stacks of magincluding a stack 10 or E-shaped laminations held together by a brass rivet H and a stack I2 01' I-shaped laminations, held together by like rivet i3. Illustratively the outer laminations'of the stack 12 have wings i4 and I! protruding upward at right angles thereto, which in the assembled unit straddle the lateral legs I and ll of the stack ll. The air gaps are located between the I-stack I2 and the contiguous ends 01' the laterallegs it and IT, and the median leg ll of the E-yoke l0. v

The present invention resides in theair gap and not in the gross structure of the inductive unit per se. The electro-magnetic coils e'ncircling various parts of the magnetic yoke are, therefore, not shown. According to this invention, the air gap is fixed anddetermined by 'an interspacer of material impervious to moisture and to impregnating fluids, of high electrical resistance, of low coefllcient oi expansion and low permeability. Preferably it is of plan area buts. small fraction of that of the airgan'so as to be traversed by but a small fraction of the magnetic flux across the air gap.

While other materials are suitable, the interspacer, is preferably a rod or length of metal wire having the properties noted, that is imperviousness to moisture, high electrical resistance, low coeillcient of expansion and low permeability. Any of a variety of metals are suitable for the purpose, including tungsten and molybdenum but high resistance alloys are in general to be preferred, such for instance as that alloy of nickel and chromium, known as Nichrome," or other alloys having electrical resistance of the same order.

In a desirable installation, the ends of the interspacer wire l9 are hooked as at 20 about diagonally opposite edges of the lateral wings I4 and I5 respectively on the I-stack, the median or eifective length 2! of the wire extending diagonally and transversely across the laminations making up the respective stacks.

With a wire of gauge somewhat larger than the air gap desired, force applied upon the assembly of Fig. 2 as for instance by a suitable clamp (not shown) and in direction lengthwise of the yoke legs, will concentrate along the lengths 2! of the interspacer wires that engage the magnetic structure with resultant high pressure thereon. Under such pressure, either the laminations or the wire will be deformed, depending upon which is softer. As shown in Fig. 5 in which the laminations are softer, the wire lengths 2i become seated in corresponding troughs 22 thus formed in the laminations. In Fig. 6 is shown the fiattening of the wire length 2| which results if the latter is materially softer than the various laminations.

In the course of assembly, the apparatus is placed in a suitable metering circuit to measure the reactance or other characteristic correlated with reactance, as the pressure is being applied, and when the desired value has been attained,

the assembly is removed from the clamp and subjected to the usual impregnation, to bond the various parts together and to fill all those parts of the air gaps not occupied by the wire with impregnating material 23.

The advantages of the present construction and method of assembly are manifest. The commercial tolerances in which the wire interspacer is made are much closer than those of paper or fiber lamination, so that wire 2| of suitable gauge can readily be selected for the assembly, dependingrupon the size of air gap desired. The accurate magnetic characteristics of the instrument being once attained, changes in the dimension of the air gap are not incurred. For the interspacer wire, does not soften or become plastic in use,

and accurately fixes the magnitude of the air gap, which remains constant in operation under the heat and magnetic pull incurred.

In operation on alternating current circuits,

' by reason of the fact that the wire interspacer is not a closed loop and by reason of the fact that the interspacer is of tremendously high resistance and small cross-section, eddy current losses therein are so small as for all practical purposes to be negligible. By reason of the low coefficient of expansion of said wire, any change in the air gap due to change in the temperature of the apparatus is also negli ible.

In its broader aspects, the invention may be carried out with the use of interspacer wire of lower resistance, especially in circuits where higher eddy current losses are not a serious factor, but where substantial constancy of the reactance value is required, 7 certain radio transmitting or receiving circuits.

. said end faces, said interspacer as for instance, in.

In certain applications, the interspacer wire might be of greater specific conductivity but of diameter so small that the linear resistance is sufiiciently high for low eddy current losses, and 5 such construction is useful especially in arrangements where the air gap is to be extremely small.

It will be noted that the wire as shown in the drawings, extends into direct contact with the 10 respective lamination ends. By reason, however, of its high resistance, there will be no consequent short circuiting disturbance. If desired, the We could be covered with a suitable coating of oxide or insulation to prevent such short-circulting.

It is obvious that the interspacer rod or wire could be arranged to extend in a spiral or in a sinusoidal or any of numerous other possible configurations between the two faces of the magnetic structure that are to be spaced thereby.

As many changes could be made in the above construction and method, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what i claim as new and desire to secure by Letters Patent of the United States is:

1. An inductive core comprising ferrous structure presenting an air gap between faces thereof and a rod-like interspacer clamped therebetween, with its length extending substantially along said faces of material impervious to moisture, having high electrical resistance and low coeflicient of expansion, and impregnating material filling that portion of the air gap not occupied by said interspacer.

2. An inductive core comprising a laminated ferrous stack structure presenting an air gap between stack end faces thereof, an interspacer affording said air gap and laterally contactin comprising a length of wire extending substantially along said faces and of the order of electrical resistance of that chrome-nickel alloy known as Nichrome, said wire being of gauge at least equal to the width of air gap desired, and means fixing said wire in position within the air gap.

3. An inductive core, comprising a laminated ferrous stack structure presenting opposed magnetic faces spaced by an air gap, an interspacer between said magnetic faces constituting the 56 means for spacing the same and definitely determining the magnitude of said air gap, said interspacer comprising a length'of round wire of metal extending along said faces, having high resistance and low coeflicient of expansion, of gauge some- 60 what larger than the'width of air gap and clamped between said magnetic faces to determine the air gap of desired dimensions, said wire extending across the lamination ends, and means retaining said wire interspacer in position against as displaoemen 4. An inductive core comprising a pair of stacks of ferrous laminations determining a magnetic frame structure with air gaps between the juxtaposed surfaces of the two stacks, wire inter- !0 spacers of high resistance extending across the air gaps and transversely of the laminated stack ends and constituting the means for spacing the same and laterally engaged by the two stack ends determining said air gaps, and means anchoring said wire interspacers in position.

5. The combination recited in claim 4 in which the wires have a low coefficient of expansion, and are anchored at their ends to the core structure.

6. An inductive core comprising two stacks of ferrous laminations assembled into a frame-like magnetic circuit with air gaps of predetermined magnitude between facing areas of said stacks, interspacers constituting the means for producing said air gap and determining the magnitude thereof, each of said interspacers comprising a length of high resistance wire of gauge somewhat larger than the magnitude of the air gap and securely clamped in position between the laminated stacks, in intimate contact with the respective laminations.

'7. The combination set forth in claim 12 in which one of the stacks of laminations comprises an I-bar extending across legs of the other stack, the extreme laminations of said I-bar having wings straddling the associated legs of the other stack, and in which the ends of therespective wire interspacers are anchored about the bases of said wings and the effective length of said wire extends diagonally between said wings.

8. An inductive core comprising two complementary stacks of ferrous laminations, one of said stacks being E-shaped, determining end legs and an intermediate leg protruding from a cross bar, the other stack being I-shaped and extending across the ends of the several legs, an interspacer between the end legs of the E-bar and the end portion of the I-bar, each of said interspacers comprising a length of high resistance wire of low coefllcient of expansion, clamped between the respective stacks and secured in place therein,

the air gap at the intermediate leg being devoid.

of interspacer.

9. In an electrical inductive apparatus, a terrous structure with faces spaced by a small air gap, an interspacer engaging and constituting .the means for spacing said faces, said interspacer comprising a length of wire of substantial speciflc conductivity but of cross-section so small as to have high linear resistance.

10. In an electrical inductive apparatus, a ferrous structure with faces parallel throughout their area and spaced by a small air gap, an interspacer engaging and constituting the means for spacing said faces, said interspacer being of a material impervious to moisture and to impregnating fluids, of high electrical resistance, of low coefficient of expansion, of small cross-section compared to the area of the faces so that the contact between the two will be only over a small area of the faces, and of such contour and hardness with respect to said faces that when the faces and the spacer are pressed together one of the two will be deformed thus seating the interspacer.

11. In an electrical inductive apparatus according to claim 10, and in which the interspacer is of such hardness with respect to said faces that when the faces and the spacer are pressed together the faces will be deformed at their points of contact with the interspacer thus seating the latter.

12. In an electrical inductive apparatus 'according to claim 10, and in which the interspacer is of such hardness with respect to said faces that when the faces and the spacer are pressed together the interspacer will be deformed and will thus be seated.

JOHN P. GLASS, JR. 

